Prior art industrial presses which include safety and fault detection systems to halt the operation of an industrial press are well-known. Of particular relevance to the present invention is the PEMSERTER(R) 1000 Press manufactured by Penn Engineering & Manufacturing Corp. of Danboro, Pa. This press heretofore has included an operator safety feature which prevents the operator's fingers from being caught between the press punch and the workpiece. The functioning of this press is described in detail in U.S. Pat. No. 4,676,421 issued to Swanstrom, which is hereby incorporated by reference as though fully set forth.
To summarize the operation of the prior art, a contact sensor located between the punch and the ram is employed in combination with a punch position sensor to establish two zones of operation. Each zone represents a portion of the ram's descent. The boundaries of the zones are determined by a programmable controller which limits the high force operation of the punch to a very small area just above the point where the punch contacts the fastener to be applied to a workpiece. An upper operator safety zone restricts this portion of the punch's descent to low pressure operation only and any contact with the punch within this portion of its stroke causes the operation of the machine to be halted and the punch to be returned fully upward to its home position. Also, if the contact is not sensed between the punch and an object within the lower high force zone, the punch also retracts. By controlling operation of the press in this way, operator safety is enhanced because the distance between the end of the punch and the fastener during the high force operation of the press is so small that it is impossible for the operator to get his fingers caught between the punch and the work.
These prior art presses, however, have serious drawbacks. Although the safety features described above protect the operator, there are no means for preventing damage to the workpiece if it is improperly located on the press anvil. Also, if a fastener is misaligned on the workpiece or mislocated with respect to the descending ram, the workpiece can likewise be damaged. In addition, the two-zone system recognizes gross workpiece or fastener misalignments as operator safety faults, thus causing the punch to retract fully to the home position. This results in a great deal of lost time.
Other prior art of which the applicant is aware includes U.S. Pat. No. 4,208,895 to Grigorenko et al; U.S. Pat. No. 4,291,359 to Dieterle; U.S. Pat. No. 4,391,358 to Haeger; U.S. Pat. No. 4,488,237 to Aronson et al; and U.S. Pat. No. 4,489,578 to Nagai et al. While these prior art patents are considered pertinent to the present invention, none is considered anticipatory of the combination of features disclosed and claimed herein. None of these references discloses a workpiece fault detection system where the press will pause only when a fault is detected using a mechanism compactly located within the ram assembly.